Method for fabricating highly conductive fine patterns using self-patterned conductors and plating

ABSTRACT

Provided is a method for forming a highly conductive micropattern, including: depositing a polymer material on a substrate; removing a portion of the polymer material to form a mask template having a dent through which a portion of the substrate is exposed to the exterior; depositing conductive ink to the top of the mask; heat treating the conductive ink in order to extract metal nanoclusters from a metallic compound dissolved in the conductive ink, wherein the portion coated with the polymer material is allowed to form an insulating pattern having electrically insulating property, while the conductive ink in the dent forms a conductive pattern having electroconductive property by the fusion of the metal nanoclusters extracted from the conductive ink; and plating a metallic material on the conductive pattern.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority under 35 U.S.C. §119 to Korean Patent Application No. 10-2009-0101313, filed on 23 Oct. 2009, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference in its entirety.

TECHNICAL FIELD

The following disclosure relates to a method for forming a highly conductive micropattern, and in particular, to a method for forming a microelectrode pattern having higher conductivity by plating a conductive pattern self-patterned through the interaction with a polymer material.

BACKGROUND

Many attempts have been made continuously to fabricate devices through printing processes in the fields of electronics and displays in order to reduce the cost needed for processing and materials and to allow mass production with ease. Many academic workers have conducted intensive studies related to such direct printing technology.

For example, active studies have conducted to fabricate electronic devices, such as RF filters based on low temperature co-fired ceramic technology, humidity sensors, organic thin film transistors, etc., through roll or ink-jet printing.

However, ink-jet printing processes using liquid ink is not suitable for the fabrication of a micropattern with a scale of several micrometers to several tens micrometers because of variations in liquid ejection condition and ejection direction caused by a wetting phenomenon at a printer nozzle. Particularly, in the case of thin film transistors requiring precise alignment between patterns, there were problems in that the resultant devices may malfunction due to the alignment error.

To solve such problems, Korean Patent Application No. 10-2009-0055437 filed by the present applicant discloses a method for forming a micropattern using a mask template. However, in this method, the polymer material forming the non-exposure section of a mask template has no hydrophobic property and is deposited on a substrate. Thus, conductive ink that functions as an electrode subsequently may infiltrate into the polymer material positioned at both sides thereof. Under these circumstances, the amount of conductive ink is reduced at the non-exposure section that has to form a conductive pattern, resulting in an increase in electrical resistance of the conductive pattern. Moreover, it is not possible for the conductive pattern to maintain a constant thickness. Further, the resultant conductive pattern having a small thickness has no sufficient conductivity.

SUMMARY

An embodiment of the present invention is directed to providing a method for forming a highly conductive micropattern by forming a conductive pattern self-patterned through the physical and chemical interaction with a polymer material and by plating the self-patterned conductive pattern to provide higher conductivity, so that such a high resistance value caused by the conductive ink lost by and infiltrated into the adjacent polymer material reduces.

In one general aspect, a method for forming a highly conductive micropattern includes:

depositing a polymer material on a substrate;

removing a portion of the polymer material to form a mask template having a dent through which a portion of the substrate is exposed to the exterior;

depositing conductive ink to the top of the mask template;

heat treating the conductive ink in order to extract metal nanoclusters from a metallic compound dissolved in the conductive ink, wherein the portion coated with the polymer material is allowed to form an insulating pattern having electrically insulating property, while the conductive ink in the dent forms a conductive pattern having electroconductive property by the fusion of the metal nanoclusters extracted from the conductive ink; and

plating a metallic material on the conductive pattern.

In one embodiment, the method for forming a highly conductive micropattern may further include removing the insulating pattern deposited on the substrate, after the plating.

In another embodiment, electroplating based on electrochemical reactions or light induced plating based on photoelectrochemical reactions may be used to carry out the plating.

In still another embodiment, the metallic material may be any one selected from silver, copper and nickel.

In still another embodiment, the substrate may be a silicon wafer and used for fabricating solar cells.

In still another embodiment, when carrying out the heat treatment, the conductive ink deposited on the polymer material may infiltrate into the interstitial spaces in the polymer material and the metal nanoclusters extracted from the conductive ink by the heat treatment may be disposed in the polymer material while being spaced apart from each other, so that the insulating pattern has electrically insulating property as a whole.

In still another embodiment, the conductive ink may be deposited on the mask template by an inkjet printing process.

In still another embodiment, when forming the mask template, laser beams may be irradiated to the polymer material to remove the polymer material.

In still another embodiment, when forming the mask template, the polymer material may be subjected to imprinting by pressurizing and heating it with a stamp so as to remove the polymer material.

In still another embodiment, the heat treatment may be carried out by heating the conductive ink and the polymer material at a temperature between 150° C. and 350° C.

In still another embodiment, the polymer material may include polyaniline.

In still another embodiment, the conductive ink may be an organometallic compound in a solution.

In yet another embodiment, the conductive ink may further include metal nanoclusters.

According to the method for forming a highly conductive micropattern disclosed herein, it is possible to reduce the electrical resistance of an electrode by plating a metallic material on the conductive pattern so as to provide higher conductivity as compared with the conductivity obtained by the fusion of the metal nanoclusters extracted through the heat treatment of the conductive ink.

It is also possible to form a microelectrode pattern while not being affected by the precision in deposition of the conductive ink on the mask template. This is because the polymer material shows insulating property by itself or through the chemical reaction with the conductive ink, and the metal nanoclusters extracted through the heat treatment of the conductive ink are prevented from fusing together by the polymer material so that they show insulating property as a whole, while the conductive ink deposited on the substrate forms a conductive pattern. Further, it is possible to reduce patterning defects by improving the insulating property between the adjacent microelectrodes.

Other features and aspects will be apparent from the following detailed description, the drawings, and the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic flow chart showing the method for forming a highly conductive micropattern according to an exemplary embodiment.

FIG. 2 is a reaction scheme illustrating the oxidation of emeraldine base-form polyaniline into pernigraniline base-form polyaniline.

FIG. 3 is a schematic view illustrating the process of extracting a metallic compound dissolved in conductive ink in the form of metal nanoclusters by heat treatment and forming a conductive pattern and an insulating pattern depending on the presence of the polymer material as shown in FIG. 1.

FIG. 4 shows a graph (portion (a)) of the surface resistance of the conductive pattern and a graph (portion (b)) of the surface resistance of the insulating pattern, after the heat treatment as shown in FIG. 1.

DETAILED DESCRIPTION OF MAIN ELEMENTS

10: substrate 20: polymer material 21: insulating pattern 30: dent 40: conductive ink 41: conductive pattern 50: metallic material 60: electrode

DETAILED DESCRIPTION OF EMBODIMENTS

The advantages, features and aspects of the present invention will become apparent from the following description of the embodiments with reference to the accompanying drawings, which is set forth hereinafter. The present invention may, however, be embodied in different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the present invention to those skilled in the art. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of example embodiments. As used herein, the singular forms “a,” “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof.

Hereinafter, exemplary embodiments will be described in detail with reference to the accompanying drawings.

FIG. 1 is a schematic flow chart showing the method for forming a highly conductive micropattern according to an exemplary embodiment. FIG. 2 is a reaction scheme illustrating the oxidation of emeraldine base-form polyaniline into pernigraniline base-form polyaniline. FIG. 3 is a schematic view illustrating the process of extracting a metallic compound dissolved in conductive ink in the form of metal nanoclusters by heat treatment and forming a conductive pattern and an insulating pattern depending on the presence of the polymer material. FIG. 4 shows a graph (portion (a)) of the surface resistance of the conductive pattern and a graph (portion (b)) of the surface resistance of the insulating pattern, after the heat treatment as shown in FIG. 1.

Referring to FIGS. 1-4, the method for forming a highly conductive micropattern according to an exemplary embodiment includes an operation S10 of depositing a polymer material, an operation S20 of forming a mask template, an operation S30 of depositing ink, an operation S40 of carrying out heat treatment, an operation S50 of plating, and an operation S60 of removing an insulating pattern.

In the operation S10 of depositing a polymer material, a polymer material 20 is deposited on the top of a substrate 10. Such deposition of the polymer material 20 is based on a coating process, such as roll coating, slit coating or spin coating in which a material is applied by centrifugal force, or a printing process such as screen printing. In this embodiment, a spin coater is set at 500 rpm to apply the polymer material 20 on the top of the substrate 10 for 20 seconds. Meanwhile, the polymer material 20 may be deposited by a spray coating process.

In this embodiment, the polymer material 20 deposited on the substrate 10 is polyaniline that is obtained in a simple manner and has excellent thermal properties as compared with other polymer materials. Polyaniline may be deposited on the substrate 10 in the form of leuco-emeraldine base, emeraldine base or pernigraniline base. However, any polymer material may be used without departing from the technical spirit of the present invention, as long as it is a particulate insulating material and shows insulating property by causing the metal nanoclusters 43 extracted from the conductive ink 40 containing a metallic material by the heat treatment to be spaced from each other.

The emeraldine base-form polyaniline is leuco-emeraldine base-form polyaniline in a partially oxidized state and has conductivity and a green color. Therefore, when the emeraldine base-form polyaniline is deposited on the substrate 10, the substrate 10 is green colored as a whole.

After depositing polyaniline on the substrate 10, polyaniline is heated at 170° C. for 5 minutes to remove the organic solvent remaining therein while increasing the resistance of polyaniline against the organic solvent.

Then, in the operation S20 of forming a mask template, laser beams with a wavelength range of about 532 nm are irradiated to the top of the polymer material 20 deposited on the substrate 10 to remove a portion of polyaniline. However, any wavelength range may be used within the scope of the present invention, as long as it doesn't damage the substrate 10 and removes the polymer material 20 with ease. The removal of the polymer material 20 provides a dent 30 through which a portion of the substrate 10 is exposed to the exterior. Herein, the dent 30 as well as the polymer material 20 that is adjacent to the dent 30 and is not removed but still remains on the substrate 10 are referred to inclusively as a mask template.

In the operation S30 of depositing ink, conductive ink 40 is deposited on the top of the mask template. In this embodiment, the conductive ink 40 is deposited on the inner part of the dent 30 by an inkjet printing process. Preferably, the nozzle section (not shown) ejecting the conductive ink 40 coincides with the path of the dents 30 in such a manner that the conductive ink 40 is filled only in the region of the dents 30. However, in general, the conductive ink 40 is deposited on the polymer material 20 adjacent to the dent 30 as well as the region of the dents 30, due to such factors as errors in devices for driving the nozzle section and variations in droplet ejection condition at the nozzle section.

The conductive ink 40 deposited according to this embodiment is provided as a solution-type organometallic silver compound obtained by dissolving a silver-containing organic compound into an organic solvent. Particular examples of the solvent used for dissolving the silver ink include polar solvents such as alcohols, or non-polar solvents such as toluene, xylene, etc., depending on the particular composition of the metallic compound. In addition, hybrid type conductive ink 40, partially containing metal nanoclusters such as silver or copper in the solution in which the metallic compound dissolved, may be used.

Various types of metallic compounds may be used in the conductive ink 40 deposited according to this embodiment. There is no particular limitation in the composition of the metallic compound, as long as the metallic compound may be extracted as metal nanoclusters by heat treatment.

In the operation S40 of carrying out heat treatment, the conductive ink 40 and the polymer material 20 are heated at a temperature ranging from 150° C. to 350° C. for an optimized time corresponding thereto, so that the polymer material 20 is converted into an insulating pattern 21 with electrically insulating property and the conductive ink 40 is converted into a conductive pattern 41 with electroconductive property. As shown in the portion (d) of FIG. 1, when carrying out the heat treatment S40, the conductive ink 40 in the dent 30 and the polymer material 20 undergo a different change.

Particularly, at the region of dents 30, metallic silver nanoclusters 43 are extracted from the organometallic silver compound ink deposited on the top of the substrate 10, and the extracted silver nanoclusters 43 are fused together to provide electroconductive property while forming a conductive network. In this manner, the silver nanoclusters 43 disposed on the substrate 10 at the region of dents 30 form a conductive pattern 41.

Meanwhile, referring to FIG. 2, the emeraldine base-form polymer material 20, i.e., polyaniline is oxidized completely into pernigraniline base-form polyaniline, at the portion on which the polymer material 20 and the organometallic silver compound ink are deposited. The pernigraniline base-form polyaniline has no electroconductivity due to its large surface resistance and shows a dark blue or black color turned from a green color.

The conductive ink 40 applied on the top of the polyaniline infiltrates into the pernigraniline base-form polyaniline, and thus the metallic silver nanoclusters 43 extracted by the heat treatment are disposed in the interstitial spaces of the polyaniline and are prevented from fusing together. As a result, it is not possible to form an electroconductive network. Therefore, since the organometallic silver nanoclusters 43 provide electroconductivity only when they are fused, they realize no electroconductivity in this case. Rather, the polyaniline and the organometallic silver nanoclusters 43 present therein form an insulating pattern 21 exhibiting electrically insulating property as a whole.

Referring to the portion (a) of FIG. 3, the conductive ink 40 deposited on the polymer material 20 infiltrates into the voids formed between the adjacent polymer materials 20. Even if highly conductive silver nanoclusters 43 are formed after the heat treatment, they are prevented from fusing together by the polymer material 20, and thus they may not form an electroconductive network. On the contrary, as shown in the portion (b) of FIG. 3, the metallic silver nanoclusters 43 extracted from the conductive ink 40 deposited on the substrate 10 at the region of dents 30 fuse together to form a highly electroconductive network.

The above-mentioned phenomenon may be determined by measuring the surface resistance values of the conductive pattern 41 and the insulating pattern 21 provided according to this embodiment. Referring to FIG. 4, the conductive pattern 41 and the insulating pattern 21 have a surface resistance of 2.57±0.06Ω/□ and 6.01±1.46Ω/□ or higher, respectively, as measured after carrying out heat treatment at 210° C. for 20 minutes.

In the operation S50 of plating, a metallic material 50 is deposited on the conductive pattern 41 via electrochemical electroplating or photoelectrochemical light induced plating. In general, since the polymer material 20 deposited on the substrate 10 does not have completely hydrophobic property, the conductive ink 40 filled in the region of dents 30 may infiltrate into the adjacent polymer material 20 during the processing. The conductive ink 40 forms a conductive pattern 41, which, in turn, is used as an electrode. Thus, such a decrease in amount of conductive ink may cause a decrease in thickness of the electrode and an increase in electrical resistance. Therefore, by plating the metallic material 50 on the conductive pattern 41, it is possible to improve the conductivity of the conductive pattern 41 that may show high electrical resistance due to a decrease in thickness caused by the infiltration of the conductive ink 40 into the polymer material 20.

In the plating operation according to this embodiment, electroplating or light induced plating is used. Electroplating is a process in which a negative electrode is connected to the conductive pattern 41 and the metallic material 50 is coated on the conductive pattern 41 under the supply of electric power. Since electroplating is widely known to those skilled in the art, detailed description thereof will be omitted herein. Light induced plating is a process in which a negative electrode is connected to the conductive pattern 41 and light is irradiated thereto to generate electromotive force so that the metallic material 50 is deposited on the conductive pattern 41.

The metallic material 50 deposited on the conductive pattern 41 may be at least one selected from silver, copper and nickel. However, various metallic materials may be used, as long as they have excellent electroconductivity, show high adhesion to the previously patterned conductive pattern 41, and exhibit strong resistance against corrosion, etc.

In the operation S60 of removing the insulating pattern, the insulating pattern 21 deposited on the substrate 10 is removed. After the removal of the insulating pattern 21, only the electrode 60 formed by the deposition of the conductive pattern 41 and the metallic material 50 remain on the substrate 10. When using the electrode for the fabrication of a solar cell, another layer, such as an anti-reflective film, may be deposited on the region from which the insulating pattern 21 is removed.

The method for forming a highly conductive micropattern according to this embodiment may be used for fabricating electronic circuit boards or the like. Particularly, in the case of light induced plating, the method may be used for fabricating solar cells. When applying the method to the fabrication of solar cells, the substrate 10 may be a silicon wafer.

In the method for forming a highly conductive micropattern according to this embodiment, when the metallic material is plated on the conductive pattern to compensate for the amount of the conductive ink infiltrating into the polymer material, it is possible to reduce the electrical resistance of an electrode.

As described above, after the heat treatment of the method for forming a highly conductive micropattern, the polymer material deposited on the substrate forms an insulating pattern by itself or through the physical or chemical reaction with the conductive ink, while the conductive ink deposited on the substrate forms a conductive pattern. In this manner, so-called self-patterning occurs by the conductive pattern and the insulating pattern realized spontaneously on the mask template. As a result, it is possible to obtain a micropattern without any defects, such as an electric short circuit, while not being affected by the precision in deposition of the conductive ink.

In the above-described embodiment, a portion of the polymer material is removed using laser beams to form a mask template. However, the polymer material may be deposited on the substrate and then subjected to imprinting to fabricate a mask template.

Further, organometallic silver compound ink is used herein as conductive ink. However, the conductive ink may include an organometallic compound, such as gold, zinc, platinum, nickel, copper, etc., depending on the particular type of the micropattern. Various types of conductive ink may be used without departing from the technical spirit of the present invention.

While the present invention has been described with respect to the specific embodiments, it will be apparent to those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the invention as defined in the following claims. 

1. A method for forming a highly conductive micropattern includes: depositing a polymer material on a substrate; removing a portion of the polymer material to form a mask template having a dent through which a portion of the substrate is exposed to the exterior; depositing conductive ink to the top of the mask template; heat treating the conductive ink in order to extract metal nanoclusters from a metallic compound dissolved in the conductive ink, wherein the portion coated with the polymer material is allowed to form an insulating pattern having electrically insulating property, while the conductive ink in the dent forms a conductive pattern having electroconductive property by the fusion of the metal nanoclusters extracted from the conductive ink; and plating a metallic material on the conductive pattern.
 2. The method for forming a highly conductive micropattern according to claim 1, which further comprises removing the insulating pattern deposited on the substrate, after said plating.
 3. The method for forming a highly conductive micropattern according to claim 1, wherein said plating is carried out by electroplating based on electrochemical reactions or light induced plating based on photoelectrochemical reactions.
 4. The method for forming a highly conductive micropattern according to claim 1, wherein the metallic material is any one selected from silver, copper and nickel.
 5. The method for forming a highly conductive micropattern according to claim 1, wherein the substrate is a silicon wafer and is used for fabricating solar cells.
 6. The method for forming a highly conductive micropattern according to claim 1, wherein when carrying out the heat treatment, the conductive ink deposited on the polymer material infiltrates into the interstitial spaces of the polymer material and the metal nanoclusters extracted from the conductive ink by the heat treatment are disposed in the polymer material while being spaced apart from each other, so that the insulating pattern has electrically insulating property as a whole.
 7. The method for forming a highly conductive micropattern according to claim 1, wherein the conductive ink is deposited on the mask template by an inkjet printing process.
 8. The method for forming a highly conductive micropattern according to claim 1, wherein when forming the mask template, laser beams are irradiated to the polymer material to remove the polymer material.
 9. The method for forming a highly conductive micropattern according to claim 1, wherein when forming the mask template, the polymer material is subjected to imprinting by pressurizing and heating it with a stamp so as to remove the polymer material.
 10. The method for forming a highly conductive micropattern according to claim 1, wherein the heat treatment is carried out by heating the conductive ink and the polymer material at a temperature between 150° C. and 350° C.
 11. The method for forming a highly conductive micropattern according to claim 1, wherein the polymer material is polyaniline.
 12. The method for forming a highly conductive micropattern according to claim 1, wherein the conductive ink is an organometallic compound in a solution state.
 13. The method for forming a highly conductive micropattern according to claim 12, wherein the conductive ink further comprises metal nanoclusters. 